Long fiber thermoplastic composite muffler system with integrated crash management

ABSTRACT

The present invention provides composite muffler systems formed of a long fiber thermoplastic. Long fiber thermoplastic technology allows the fibers, to maintain a length sufficient to provide structural strength at lower fiber loading. The long fiber thermoplastic material for forming composite muffler systems also provides increased impact strength and creep resistance as well as chemical and thermal resistance. Mufflers molded with long fiber thermoplastics demonstrate improved dimensional stability as compared to known short fiber based moldings. One suitable muffler structure is a multi-piece muffler assembly including at least one long fiber thermoplastic shell section. In accordance with the present invention, the long fiber thermoplastic material and moldings may also be combined with over-molding of preforms of unidirectional or woven inlays, which provide local structural performance. The use of such preforms is particularly suited to use in the manufacture of high temperature, structural articles such as bumper muffler combinations.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates to composite muffler systems includinglong fibers to provide structural integrity. The mufflers may be moldedinto shape that allow for their use in confined spaces within a motorvehicle or in combination with a facia to form a part such as bumpers,rocker panels, air dams, spoilers, sideboards and body modules.

SUMMARY OF THE INVENTION

The present invention provides composite muffler systems formed of along fiber thermoplastic material. Long fiber thermoplastic technologyallows the fibers to maintain a length sufficient to provide structuralstrength at lower fiber loading. The long fiber thermoplastic materialfor forming composite muffler systems also provides increased impactstrength and creep resistance as well as chemical and thermalresistance. Mufflers molded with long fiber thermoplastics demonstrateimproved dimensional stability as compared to conventional short fiberbased moldings. One suitable muffler structure is a multi-piece mufflerassembly including at least one long fiber thermoplastic shell section.In accordance with the present invention, the long fiber thermoplasticmaterial and moldings may also be combined with over-molding of preformsof unidirectional or woven inlays, which provide local structuralperformance. The use of such preforms is particularly suited for use inthe manufacture of high temperature, structural articles such as bumpermuffler combinations.

The long fiber thermoplastic molding for composite mufflers of thepresent invention allows for complex geometry and part integrationreducing assembly steps, and shapes to match vehicle design space eitheras separate unit or integrated into other vehicle components such asbumper systems, air dams, wheel wells, rocker panels, and others,providing packaging space reduction and better economics and improvedproperties than prior art methods. The combination of long fiberthermoplastics with filling systems and in addition combined withintegrated airflow promoting features allows for reduced surfacetemperature which further reducing the need for heat shielding that istypical in cars as well as a reduction in packaging space. Otherfeatures can also be integrated such as underbody protection functionsand attachment features to the car body.

The use of long fiber thermoplastics based articles allows for the useof a range of molding technologies such as injection molding andcompression molding with long fiber thermoplastic pellets as input. Itis also possible to use direct compounding variants of the pellets orcompression molding of pre-compounded sheets using either random fibersor sheets based on woven fibers and hybrids. The fibers are typicallyglass based but may alternatively be carbon, mineral, natural, steel,copper, other metal or synthetic fibers such as aramids.

The use of long fiber thermoplastic materials allows for the manufactureof intricate design details and allows the use of several muffler shellconnecting methods. The design with long fiber thermoplastic materialsis particularly suited for stacked assembling of the components allowinghigher efficiency and potential for automated assembly.

In accordance with a first aspect of the present invention, a mufflerassembly is provided as a part of a motor vehicle component such as abumper, rocker panel, air dam, or sideboard. The muffler having an outershell formed from a long fiber thermoplastic composite material that mayform part of the component or be formed to conform to the outer facia ofsuch a component. That is, the muffler may be a separate element fromthe component coupled thereto or is formed as an integral part of thecomponent. The perforated pipe may include openings formed by completelyremoving small metal portions from the pipe. Alternatively, theperforated pipe may comprise a louvered pipe, wherein the openings areformed by cutting and subsequently bending small sections of the pipeoutwardly. While a straight, flow through pipe is shown in the figures,for simplicity, the pipe may include bent sections to form an s-curve orother complex curve within the muffler assembly.

The muffler further comprises a perforated pipe for receiving exhaustgases, and fibrous material provided within the outer shell between theperforated pipe and the outer shell. The fibrous material may be formedof multiple material preforms that are received respectfully in thefirst and second shell parts. Alternatively, the fibrous material maycomprise a loose or bagged ‘texturized’ wool-type product providedwithin an internal cavity of the outer shell. It is also contemplatedthat the fibrous material may be a mat product wrapped about theperforated pipe or otherwise filling the internal cavity of the outershell. It is also contemplated that combinations of these filltechniques may be used. For example, a mat product may be installedwithin the shell to act as a secondary heat and air insulator sectionwhile the primary insulation is a preform or a form of ‘texturized’ woolinstalled between the mat and the pipe.

The muffler assembly may further comprise a heat shield positionedbetween the muffler outer shell and the exhaust pipe. It may alsocomprise at least one bushing for holding a portion of the perforatedpipe within the outer shell. The bushings may serve several tasksincluding acting as a heat sink to reduce the temperature of the pipe,as a vibration absorber to reduce the physical stress transmitted fromthe engine to the muffler shell or as a structural reinforcement thatact as part of the motor vehicle crash management system. The mufflertypically a main body having front, rear, upper and lower surfaces. Aportion of the main body may define at least a part of an outer shell ofthe muffler as well as a facia, or aesthetic surface, of the motorvehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is an exploded perspective view of a thermoplastic muffler inaccordance with the present invention.

FIG. 1A is a partial cross-section of a muffler according to the presentinvention taken along line A-A of FIG. 1.

FIG. 2 is an exploded perspective view of a thermoplastic muffler inaccordance with the present invention.

FIG. 2A is a cross-sectional view taken along line A-A of FIG. 2

FIG. 2B is a detailed perspective view of the opposite side of themuffler of FIG. 2

FIG. 3 is an exploded perspective view of a thermoplastic muffler inaccordance with the present invention.

FIG. 4 is a cross-sectional view of a muffler and integrally formedimpact member, in accordance with the present invention.

FIG. 5 is a perspective view of a muffler shell according to the presentinvention and showing an optional insulating blanket.

FIG. 6 is a perspective view of a commercial truck showing optionalhorizontal and vertical muffler assemblies, in accordance with thepresent invention.

FIG. 7 is a plan view of a direct compounding long fiber thermoplasticextruder, useful in manufacturing a muffler in accordance with thepresent invention.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION

A long fiber thermoplastic composite muffler 100 according to thepresent invention is shown in FIG. 1 including first and second outershells 112A and 112B, a porous pipe 114 and entry bushing 116 and exitbushing 118 for fluid communication of exhaust from an internalcombustion engine to the interior of the chamber 110 via orifices 120and then to the atmosphere.

As shown in FIG. 1 the first and second outer shells 112A, 112B may beshaped to fit within a space under a vehicle body. A baffle 122 may beincluded within the chamber of the muffler 100. The baffle separates theinterior of the shell into discrete zones and serves to improve theacoustical performance of the muffler and may optionally be perforatedto allow fluid communication between the discrete zones formed by thebaffle 122. The chamber may be filled with a fibrous absorber (notshown) between the porous pipe 114 and the inner surface of the mufflerchamber 110. Such absorptive silencers efficiently reduce acousticalenergy by the sound absorbing characteristics of the sound absorbingmaterial. As shown in FIG. 1A, the bushing 116 may be shaped to includea sinusoidal or other formed increased surface area act as heat sink toreduce the temperatures to suitable levels at the metal polymerinterface. The shells 112A, 112B include a flange 124A to receive theouter edge 126 of bushing 116. The coupling between edge 126 and flange124A may include a seal 128, preferably formed of a flexible hightemperature seal such as Viton (available from duPont of Wilmington,Del., USA) or a silicone based sealant. The seal 128 further reduces thetemperature of the bushing 116 at flange 124A, provides tolerancecompensation and compensates for differential coefficient of thermalexpansion. The seal 128 may be placed on the bushing 116 as a singlering or may be molded into the muffler shells. While a rectangularflange 124A is shown, the interface may have any suitable geometry thatprovides sealing and positioning. The bushing interface geometry istypically circular shape perpendicular to the exhaust pipe but can alsohave other shapes or positions.

As seen in FIG. 1, first shell 112A preferably includes a flange 124A atthe entrance end of the muffler 100 and a second flange (not shown) atthe exit end of the muffler. The second shell 114B preferably includes aflange 124B at the entrance end of the muffler 100 and a second flange130 at the exit end of the muffler. In accordance with on embodiment ofthe invention, the first shell 112A may include a molded flange 132A andthe second shell 112B may include a molded flange 132B to receive theouter edge of baffle 122. The molded flanges 132A, 132B may include aseal (not shown) similar to seal 128. The muffler 100 may include an airguide 136 on the leading edge of the muffler 100 to increase airflowtoward the bushing 116. The increased airflow and cooling is beneficialat the upstream bushing 116 because the upstream bushing 116 is closerto the engine and thus operates at a higher temperature than bushing118. A heat sink 117 may optionally be added to the exhaust pipe 114 outside of the muffle 100 to decrease the temperature at bushing 116.

In accordance with the present invention, the muffler 100 is assembledto include porous pipe 114 and baffle 122. The shells 112A, 112B arebrought together so that edges 134A, 134B are in contact. The edges134A, 134B may then be bonded by a variety of methods such as thermalbonding, ultrasonic welding, laser welding, and adhesives or may bemechanically coupled by a snap fit mechanism or a number of hooks.

The assembled muffler 100 may have cavity 110 filled with a fibrousthermal and acoustical insulation (not shown) by any number of methodsknown to those skilled in the art. For example in a direct fill method,a plurality of filaments that are separated or texturized viapressurized air to form a loose wool-type product in the outer shell112A, 112B, see U.S. Pat. Nos. 5,976,453 and 4,569,471, the disclosuresof which are incorporated herein by reference. The muffler 100 mayinclude a port 142 for receiving the insulation and a cap 142 forsealing port 142. Cap 142 may be secured to the port by any suitablemethod such as chemical bonding, welding or mechanical attachment.Another suitable method for installing insulation is to include apreformed fibrous insulation insert, placed into cavity 110 duringassembly. Processes and apparatus for forming such preforms aredisclosed in U.S. Pat. Nos. 5,766,541 and 5,976,453, the disclosures ofwhich are incorporated herein by reference; and in patent application,U.S. Ser. No. 08/802,492, the disclosure of which is also incorporatedherein by reference.

One suitable absorptive silencer is a fibrous glass insert. The strandis preferably a glass fiber with a relatively high resistance to thermaldegradation such as A glass, Standard E glass, S glass, T glass, ECRglass, Advantex® (Calcium-Aluminum-Silicate glass), ZenTron™ glass orany other filler composition with suitable strength and thermalproperties to withstand the thermal and physical stresses inherent in amuffler. The fibrous material may comprise first and second fibrousmaterial preforms which are received respectfully in the first andsecond shell parts. Alternatively, the fibrous material may comprise aloose or bagged fluffed-up, wool-type product provided within aninternal cavity of the outer shell. It is also contemplated that thefibrous material may comprise a mat product wrapped about the perforatedpipe or otherwise filling the internal cavity of the outer shell.

It is also contemplated that ceramic fiber material may be used insteadof glass fibrous material to fill the outer shell 112A, 112B. Ceramicfibers, if continuous, could be filled directly into the shell or usedto form a preform that is subsequently placed in the shell 112A, 112B.It is also contemplated that preforms may be made from a discontinuousglass fiber product produced via a rock wool process or a spinnerprocess used to make fiberglass used as thermal insulation inresidential and commercial applications. It is further contemplated thatstainless steel could be wrapped about the perforated pipe 114 or madeinto a cylindrical preform and then slipped over the pipe 114 prior tothe pipe 114 being inserted into the outer shell. It is additionallycontemplated that an E-glass needle felt mat, made into a cylindricalpreform, and slipped over the perforated pipe 114. A layer of stainlesssteel could be provided between the needle felt mat preform and theperforated pipe 114.

As shown in FIG. 2, a muffler-bumper assembly 200, in accordance withthe present invention may include at least a bumper facia 202 formed ofa long fiber thermoplastic material or of a standard automotive faciamaterial such as sheet molding compound or bulk molding compound. Facia202 provides a cavity, which encloses exhaust pipe 204 and bushings210A, 210B. The entry bushing 210A and the exit bushing 210B may beshaped to include a sinusoidal or other form to increase surface area toact as a heat sink. As discussed above the facia may include a flange(not shown) to receive the bushings 210. The coupling between facia 202and bushings 210 preferably include a flange (not shown) and a flexiblehigh temperature seal (not shown). The exhaust pipe 206 may include aflexible coupler 208 to isolate vibration and noise from the engine anda tailpipe 212 for venting exhaust to the atmosphere.

In one embodiment of the invention, the bushings 210A, 210B and theinternal muffler baffles 216 may be corrugated to act as energyabsorbing crumple members to meet bumper crash requirements. The mufflerassembly may also include an air-guide 214. Air-guide 214 increases theflow of air across the muffler assembly 200 to lower the temperature ofthe assembly.

FIG. 2A shows an assemble cross-section of a bumper muffler assembly200, taken along line A-A, in which the exhaust pipe 204 and internalbaffles 216 provide structural integrity to bumper muffler assembly 200.The assembly includes a first shell 202, which acts as a facia for amotor vehicle and a second shell 214. The assembly 200 also includes afirst fibrous preform 215B and a second fibrous preform 215B. Alsoincluded is a fibrous mat 217 to provide additional thermal insulationbetween pipe 204 and first shell 202, mat 217 may be beneficial toinhibit blistering on the facia or to limit hotspots on the bumper 200,where it may contact the legs of an individual loading a trunk. Alsoshown is an inlay 207 to reinforce the area at external ribbing pattern205. Inlay 207 may be place in the mold used to form shell 202. Inlay207 provides additional strength to at least portions of the shell.Inlay 207 may be in the form of a woven or non-woven fibrousreinforcements.

FIG. 2B shows a perspective view of the first shell 202 including anexternal ribbing pattern 205 to increase the structural integrity andimpact strength of the shell and hence the muffler assembly.

As shown in FIG. 3, a muffler-bumper assembly 230, in accordance withthe present invention may include at least a bumper facia 240 formed ofa long fiber thermoplastic material or of a standard automotive faciamaterial such as sheet molding compound or bulk molding compound. Facia240 typically provides a non-structural, aesthetically pleasing surface.The muffler 232 is fed by exhaust pipe 234 and vents exhaust to theatmosphere by tailpipe 236. The structure may be similar to thatdisclosed above, or the muffler assembly 232 may be suspended from thestructural bumper member 238. FIG. 3A shows a cross-section of a bumpermuffler assembly 230, in which the exhaust pipe 234 and muffler 232 aresuspended from the structural impact member 234. Muffler assembly 230may optionally be formed with and air-guide (not show) which may beintegrally molded with muffler 232 or may be a separately formed piece.

FIG. 4 shows a muffler assembly 250 in accordance with the presentinvention, in which the structural impact member 252 and the muffler 256are molded and the exhaust pipe 254 is subsequently installed. The facia258 may be formed of any suitable material because little strength isrequired. Muffler assembly 250 may optionally be formed with andair-guide 260 integrally molded. While the muffler 256 is shown as aunitary molding with the impact member 252 in FIG. 4 it would be equallypossible to form the muffler assembly 256 as a separate unit forsubsequent connection with the impact member 252. As shown in FIG. 2Aand FIG. 2B it is also possible to form the muffler assembly 200 so thatthe exhaust pipe 204 forms the impact member.

As shown in FIG. 5, a mat 150 formed of glass fibers or other suitablehigh temperature acoustic and thermal insulating material may be placedat the interior surface of shell 112B (as well as in opposing shell 112A(not shown)). Mat 150 serves as an airflow diffuser to avoid hot spotsand to provide an even temperature load distribution. The mat mayinclude a thin metal reflective or other heat protecting film. Mat 150mat be fixed to shell 112B by features molded into the shell, by anadhesive or by the insertion of the fibrous insulator 152 (as seen inFIG. 5B).

As shown in FIG. 6, a commercial truck may include a muffler of thepresent invention in the form of a side board or rocker panel assembly282 or as an air dam or spoiler 284.

For the purposes of the present invention, the term long fiberthermoplastic material is a material including an initial glass fiberinput that is longer than 4.5 mm. There are a variety of forming methodsfor long fiber thermoplastics, the two most common being pelleting anddirect compounding. In direct compounding, a roving is used as an inputand the initial glass input is chopped to length during the mixing ofthe fibers with a polymer melt. Preferably, the long fiber thermoplasticmaterial has at least 5% weight of the glass fiber fraction of thematerial has a mean (average) Length/Diameter ratio (L/D) greater than35 in the molded product.

One suitable process for preparing long fiber thermoplastic materials isa so called wire coating process, as disclosed in U.S. Pat. No.5,972,503, entitled “Chemical Treatments for Fibers and Wire-CoatedComposite Strands for Molding Fiber-Reinforced Thermoplastic CompositeArticles” and herby incorporated by reference. In a wire coating processwire coater is fed molten polymeric material by a conventional extruderto encase a preimpregnated glass strand. The wire coater includes a diehaving an exit opening for shaping the sheath into a desired thicknessand/or cross-section. The encased strands may then be chopped to apredetermine length.

Another suitable process is a direct compounding method in which glassroving is added to a premelted thermoplastic compound. In the directcompounding process, as shown in FIG. 7 thermoplastic resin, preferablyin the form of pellets, is provided to resin primary extruder 12 from aresin supply 14. The resin may be any of a variety of acceptablethermoplastic resins for the product purpose intended, such as, nylon,thermoplastic polyurethane, and polyesters. A melting screw 16 rotateswithin melting barrel 18 of extruder 10. While the shear force ofmelting screw 16 may provide sufficient heating to melt and conditionthe polymer, the melting barrel 18 may be provided with an additionalheat source as is known in the art.

A flow control plate 20 may be used at the downstream end of barrel 40to control the flow of resin 15 out of the extruder barrel 18 and intocoating die 22. The plate 20 typically restricts the flow of resin 15 bya reduction in the diameter or by otherwise constricting the flow withinthe barrel 18. The coating die 22 and any apparatus in contact with theresin 15 may include suitable heat elements to maintain the desiredtemperature of the resin. The pressure within the coating die may bemonitored by a pressure transducer that provides a control signal to thedrive motor 17 of melting screw 16.

Fiber spool 24 provides a direct feed of a tow of structural reinforcingfibers 26. The fibers are pulled though injection nozzle 28 into thecoating chamber 32 of coating die 22. The fibers 26 are then intimatelyblended and coated with the molten polymer material 15. The coatedfibers 26 then exit the coating die 22 through die orifice 36 ofinterchangeable insert 30. The diameter of the die orifice 36 canadjusted by changing insert 30 to control the ratio of fibers 26 toresin 15.

The resin 15, fiber 26 mixture exits coating die 22 and the fibers 26may be cut by blade 52 in cutting chamber 50 in housing 54, 56. Themixture of resin 15 and fibers 26 exit chamber 50 via orifice 58 intoextruder 60. The extruder 60 typically includes a barrel 62 that feedsthe mixture of resin 15 and fibers 26 into extrusion die 64. A feedscrew 66 rotates with barrel 62 and may optionally reciprocate alongaxis 72 to feed a charge of molding material through orifice 63 into themolding cavity 68 of die 64. The feed screw 66 is driven by a power unit70.

The temperature within the barrel 18, coating chamber 32, cuttingchamber 50 and extruder 60 may be controlled by one or more heatingelements and temperature probes controlled a microprocessor (not shown).

Suitable polymers include thermoplastic polymers such as polyamide (PA6,PA66, PA46, PA11, PA6.12, PA6.10 & PA12), aromatic polyamides,polyphenylene ether (PPE) and polyamide blends, blends of polyphenyleneether (PPE) and epoxy, polyetherimide (PEI) and blends thereof such asPEI/silicone, polyethersulphone (PES), polysulfone (PSU),polyethersulfone (PES), polyphthalamide (PPA), polyphenylenesulfide(PPS), syndiotactic polystyrene (SPS), liquid crystal polymer (LCP),polybutylene terephthalate (PBT), polyethylene terephthalate (PET),thermoplastic polyurethane (TPU), polytetrafluoroethylene (PTFE),poly(vinylidene fluoride) (PVDF), polyetherketone (PEK),poletheretherketone (PEEK), aliphatic polyketone (PK), high heatpolycarbonate grades (such as Tough Z HR Grade, available from IDEMITSUKOSAN, Japan) as well as other thermoplastic materials have suitablemechanical, thermal and melt flow properties. Another class of suitablethermoplastic polymers are so called ceramifiable thermoplastic polymerswhich may be formed as a conventional thermoplastic polymer but whenheated form a material similar in properties to a ceramic material.

The invention of this application has been described above bothgenerically and with regard to specific embodiments. Although theinvention has been set forth in what is believed to be the preferredembodiments, a wide variety of alternatives known to those of skill inthe art can be selected within the generic disclosure. The invention isnot otherwise limited, except for the recitation of the claims set forthbelow.

1. A fiber reinforced polymer muffler having improved properties,comprising: a fiber reinforced thermoplastic polymer shell having glassfiber weight fractions range from 5% to 90%, said shell including afirst least one shell portion: an exhaust duct for carrying exhaustgasses through said polymer shell; and a fibrous dissipative silencer.2. The fiber reinforced polymer muffler of claim 1, wherein at least 5%weight of the glass fiber fraction has a mean Length/Diameter ratio(L/D) greater than
 35. 3. The fiber reinforced polymer muffler of claim1, wherein the fibrous dissipative silencer is a selected from the groupconsisting of A glass, Standard E glass, S glass, T glass, ECR glass,Calcium-Aluminum-Silicate glass, S-2 glass and mineral wool.
 4. Thefiber reinforced polymer muffler of claim 1, further comprising a mat offibrous material between said shell and said exhaust duct.
 5. The fiberreinforced polymer muffler of claim 4, further comprising a facingselected from the group consisting of heat resistant and thermalreflective facings.
 6. The fiber reinforced polymer muffler of claim 1,further comprising: a metallic heat sink on said exhaust duct.
 7. Thefiber reinforced polymer muffler of claim 1, wherein said thermoplasticis a ceramifiable polymer.
 8. The fiber reinforced polymer muffle ofclaim 1, wherein said thermoplastic is selected from the groupconsisting of polamides, aromatic polyamides, polyetherimides,polyethersulfones, polysulfones, polyphthalamides, blends ofpolyphenylene ether and epoxy, polyphenylsulphones, syndiotacticpolystyrenes, liquid crystal polymers, polybutylene terephthalates,polyethylene terephthalates, thermoplastic polyurethanes,polytetrafluoroethylenes, polyvinylidene fluorides, polyetherketone,polyetheretherketones, aliphatic polyketone and polycarbonates andblends thereof.
 9. The fiber reinforced polymer muffler of claim 1,further comprising at least one internal baffle.
 10. The fiberreinforced polymer muffler of claim 9, further comprising a plurality ofinternal baffles.
 11. The fiber reinforced polymer muffler of claim 9,wherein said at least one internal baffle is perforated.
 12. The fiberreinforced polymer muffler of claim 1, further comprising an airguide.13. The fiber reinforced polymer muffler of claim 1, further comprisingan external ribbing pattern.
 14. A molded fiber reinforced polymermuffler having improved properties, comprising: a fiber reinforcedthermoplastic polymer shell including a first least one shell portion:an exhaust duct for carrying exhaust gasses through said polymer shell;a fibrous dissipative silencer; and a mat of fibrous material betweensaid shell and said exhaust duct.
 15. The fiber reinforced polymermuffler of claim 14, further comprising a facing selected from the groupconsisting of heat resistant and thermal reflective facings.
 16. Thefiber reinforced polymer muffler of claim 14, further comprising: ametallic heat sink on said exhaust duct.
 17. The fiber reinforcedpolymer muffler of claim 14, further comprising: a reinforcing inlaymolded into said polymer shell.
 18. The fiber reinforced polymer mufflerof claim 14, further comprising: an airguide integrally molded with saidat least on shell portion.
 19. The fiber reinforced polymer muffler ofclaim 14, further comprising an external ribbing pattern.
 20. A fiberreinforced polymer muffler having improved properties, comprising: afiber reinforced thermoplastic polymer shell having glass fiber weightfractions range from 5% to 90%, said shell including a first least oneshell portion wherein at least 5% weight of the glass fiber fraction hasa mean Length/Diameter ratio (L/D) greater than 35, wherein saidthermoplastic is selected from the group consisting of polamides,aromatic polyamides, polyetherimides, polyethersulfones, polysulfones,polyphthalamides, blends of polyphenylene ether and epoxy,polyphenylsulphones, syndiotactic polystyrenes, liquid crystal polymers,polybutylene terephthalates, polyethylene terephthalates, thermoplasticpolyurethanes, polytetrafluoroethylenes, polyvinylidene fluorides,polyetherketone, polyetheretherketones, aliphatic polyketone andpolycarbonates and blends thereof; an exhaust duct for carrying exhaustgasses through said polymer shell; and a fibrous dissipative silencer; amat of fibrous material between said shell and said exhaust duct; afacing selected from the group consisting of heat resistant and thermalreflective facings.